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Re: st: set obs by level (of multiple variables)?


From   Rebecca Pope <rebecca.a.pope@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: set obs by level (of multiple variables)?
Date   Thu, 17 Jan 2013 10:30:56 -0600

bysort TCATOG sex : gen first2 = (_n==1)

That tests whether it is the first observation or not & returns 1 if
true, 0 otherwise.

On Thu, Jan 17, 2013 at 10:24 AM, Tim Evans <Tim.Evans@wmciu.nhs.uk> wrote:
> Nick thanks for your help. This does what I need, although, rather than duplicating the last record, duplicating the first might be more helpful as this would contain much of the baseline information I already hold. I naively thought that this would work!!:
>
> bysort TCATOG sex : gen first2 = _n - but I have 1-20 rather than 1 followed by 0
>
> I could then use replace first2 = 0 if first !=1 - but I'm assuming there is a better way?
>
> Best wishes
>
> Tim
>
>
>
>
> -----Original Message-----
> From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
> Sent: 17 January 2013 15:53
> To: statalist@hsphsun2.harvard.edu
> Subject: Re: st: set obs by level (of multiple variables)?
>
> The syntax diagram for -set- does not indicate support for -by:- and
>
> 1. Whatever is not permitted should be considered forbidden.
>
> 2. Less gnomically, there is a really good reason for this. In essence, -set- is about global settings, and even if what you are asking for makes sense -- as it does here -- -set- and -by:- don't mix naturally.
>
> See help for -expand-, -expandcl-, -expandby- (SSC).
>
> bysort stage sex : gen last = _n == _N
> expand 2 if last
> sort stage sex
> ... if last
>
> On Thu, Jan 17, 2013 at 3:08 PM, Tim Evans <Tim.Evans@wmciu.nhs.uk> wrote:
>
>> I'm trying to insert extra observations in my dataset - I've calculated survival and wish to graph the results but the data start from less than 100%, but I'd like the graph to graph from time 0 and thus 100%. My dataset is split by gender and stage so I need something that inserts an observation for say males & stage 1, males stage 2, females stage 1 and females stage 2.
>>
>> Unfortunately, while this will provide me with an observation
>>
>> set obs `=_N+1' it does not support this:
>>
>> bysort stage sex: set obs `=_N+1'
>>
>> Does anyone have an idea how I might do this in Stata 11.2?
>
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